A known impact absorbing device for use with a car seat belt is shown in German Patent DT-PS No. 1,245,223. This device is comprised of a tubular housing having a conical or tapered bore which receives a conical insert. Upon impact, or rapid deceleration, the conical insert locks in the conical bore and cannot, under normal conditions, be unlocked manually from the locked position. Thus, the assembly is rendered useless until it is repaired in a repair shop. While the adjustment means remains unrepaired, the seat belt is not snug which, however, it should be in order to be effective in preventing serious injuries during an accident. Once locked, the device does not allow for some movement by the user. Another drawback of this device resides in the abrupt locking response during impact leading to potentially severe injuries to the user.